1. Field of the Invention
The present invention relates to novel homogeneous copolyetheramide block polymers which have, in particular, a high crystallinity such as to provide high melting points and a good mechanical resistance to heat, the lowest possible glass transition temperature such as to provide substantial flexibility and elasticity at temperatures as low as -20.degree. C. or below, and a high viscosity in the molten state, which is compatible with ease of use in the fields of injection molding and extrusion.
2. Description of the Prior Art
U.S. Pat. No. 4,218,351 describes thermoplastic elastomers consisting of copolyetheramides. In this patent, a general family of copolyetheramides is proposed, the polymers being obtained by the direct reaction of three types of constituents, each possessing functional groups capable of participating in a reaction which produces amide groups. The first constituent (i) is selected from the group comprising a short-chain dicarboxylic acid, a short-chain diamine, a short-chain lactam, a short-chain aminoacid and a mixture of two or more than two of these species with one another; the second constituent (ii) is a fatty acid dimer or an amino derivative of a fatty acid dimer; and the third constituent (iii) is a polyoxyalkylenediamine or a polyoxyalkylenedicarboxylic acid. The constituents participating in the reaction are selected such as to introduce approximately equivalent quantities of NH.sub.2 and COOH groups into the medium. From the examples in the aforesaid '351 patent, it is noted that the copolyetheramides which are in fact prepared are essentially obtained by reacting (i) a mixture of a short-chain diacid and a short-chain diamine, or a mixture of a lactam and a short-chain diacid or a short-chain diamine, with a reactant of type (ii) and a reactant of type (iii). The copolyetheramides prepared in this manner have valuable properties, in particular flexibility at low temperature, which is responsible for the good impact strength properties stated. However, their low viscosity in the molten state, which is generally less than 100 poises at 232.degree. C., enables them to be used only as adhesives. Now, in the fields of molding and extrusion of plastics, materials are required which have a sufficiently high viscosity in the molten state as to permit them to be injection-molded or extruded in appropriate fashion. The prior art does not even allude to means which make it possible to obtain, starting from the reaction mixtures according to the teaching of the above-mentioned '351 patent, copolyetheramides possessing a sufficiently high viscosity in the molten state to permit their use as technical-grade plastics.